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Science 29 September 2006:
Vol. 313. no. 5795, pp. 1945 - 1948
DOI: 10.1126/science.1131536
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Reports

Ultrafast Vibrational Dynamics at Water Interfaces

John A. McGuire* and Y. Ron Shen{dagger}

Time-resolved sum-frequency vibrational spectroscopy permits the study of hitherto neglected ultrafast vibrational dynamics of neat water interfaces. Measurements on interfacial bonded OH stretch modes revealed relaxation behavior on sub-picosecond time scales in close resemblance to that of bulk water. Vibrational excitation is followed by spectral diffusion, vibrational relaxation, and thermalization in the hydrogen-bonding network. Dephasing of the excitation occurs in ≤100 femtoseconds. Population relaxation of the dangling OH stretch was found to have a time constant of 1.3 picoseconds, the same as that for excitation transfer between hydrogen-bonded and unbonded OH stretches of water molecules surrounded by acetone.

Department of Physics, University of California, Berkeley, CA 94720, USA. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.

* Present address: Chemistry Division, C-PCS, MS-J567, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.

{dagger} To whom correspondence should be addressed. E-mail: yrshen{at}calmail.berkeley.edu

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Science. ISSN 0036-8075 (print), 1095-9203 (online)